Real-time image contrast and edge sharpness enhancing apparatus

ABSTRACT

Apparatus for enhancing contrast and edge sharpness of images visually displayed by a line scan imaging and display system wherein an electrical analog output signal of a line scan imaging system which may be degraded is processed in real time by enhancing circuitry producing corrective signals of adjustable magnitude for addition to the degraded signal to provide an enhanced brightness intensity modulating signal for a video display. The enhancing circuitry includes differentiating circuitry for obtaining the first and second derivatives of the degraded signal in turn applied to enhancer circuitry for causing the polarity of the first derivative to be always opposite to that of the second derivative so that the relative amplitudes of higher frequencies are emphasized. The polarity adjusted first derivative is added to the degraded signal to make the displayed image more crisp by reason of enhanced edge sharpness. A second polarity adjusted signal is developed by causing the polarity of the degraded signal to follow that of the first derivative. An integration of the second polarity adjusted signal wherein the relative amplitude of low frequencies are emphasized is added to the degraded signal to enable a visual display of greater contrast.

Unite States Patent Beck [54] REAL-TIME IMAGE CONTRAST AND EDGESHARPNESS ENHANCING APPARATUS [72] Inventor: Cyrus Beck, Abington, Fav

[731 Assignee: The United States of America as representedbytheSecretary of the Navy [221 Filed: July 24,1969

[21] Appl.No.: 844,540

Primary ExaminerRobert L. Griffin Assistant ExaminerRichard P. LangeAtt0rney Edgar J. Erower, Henry Hansen and B. Frederick Buchan, Jr.

[ ABSIRACT Apparatus for enhancing contrast and edge sharpness of imagesvisually displayed by a line scan imaging and display system wherein anelectrical analog output signal of a line scan imaging system which maybe degraded is processed in real time by enhancing circuitry producingcorrective signals of adjustable magnitude for addition to the degradedsignal to provide an enhanced brightness intensity modulating signal fora video display. The enhancing circuitry includes differentiatingcircuitry for obtaining the first and second derivatives of the degradedsignal in turn applied to enhancer circuitry for causing the polarity ofthe first derivative to be always opposite to that of the secondderivative so that the relative amplitudes of higher frequencies areemphasized. The polarity adjusted first derivative is added to thedegraded signal to make the displayed image more crisp by reason ofenhanced edge sharpness. A second polarity adjusted signal is developedby causing the polarity of the degraded signal to follow that of thefirst derivative An integration of the second polarity adjusted signalwherein the relative amplitude of low frequencies are emphasized isadded to the degraded signal to enable a visual display of greatercontrast.

. 3 Drawing n f I 22 23 i LINE SCAN I y y i SYSTEM 1 25 s 26 A f HARDF31 umren 46 I 30/- l l HARD 47 as l l LIMITER VARIABLE L 31 36 y, emsHARD 1 j r 2 ADJUSTER I I 1 32 l Y z HARD W LIMITER 35 AND 36 48OPPOSITE EXCL. -l POLAR/TY on A13 43 l 0rcr0R lv SAME LINE SCAN iPOLAR/T) DISPLAY POLARITY 4o 24;] 0575570 REVERSING 2 39 SWITCH vPOLARITY REVERSING swncu INTEGRATOR CO/WRAST ENHANCE? EDGE swamENHANCE/P f ENHANCING CIRCUITRY SHEET 2 OF 3 TIME TIME F T/ME y (WHEN a0) TIME = T/ME INVENTOR.

CYRUS BECK sum 3 OF 3 y (WHEN ,8 =0) Fig. 3

2: TIME T/ME T/ME y (WHEN a O) T IME INVENTOR.

CYRU S BECK REAL-TIME IMAGE CONTRAST AND EDGE SHARPNESS ENHANCINGAPPARATUS STATEMENT OF GOVERNMENT INTEREST The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention generally relates to displaysand, more particularly, relates to means for enhancing degraded outputBRIEF SUMMARY OF THE INVENTION Accordingly, it is the general purpose ofthe invention to provide means for enhancing not only edge sharpness butalso relative contrast in a visual representation of an image asestablished by a brightness intensity modulating electrical signal suchas the output signal of a line scan imagining system.

The general purpose and other objects of the invention are brieflyaccomplished by providing enhancing circuitry operable to developcorrective signals in real time from a degraded signal a first of whichemphasizes the amplitudes of lower frequencies and a second of whichemphasizes the amplitudes of higher frequencies. The inventioncomprehends differentiating circuitry for providing the first and secondderivatives of the degraded signal and an edge sharpness enhancer havinga polarity detector driving a polarity reversing switch so that thecorrective output signal therefrom generally represents the magnitude ofthe first derivative in real time which continually has been adjusted tohave a polarity opposite that of the second derivative. The inventionalso comprehends a contrast enhancer including a detector for comparingthe polarities of the first derivative and the degraded signal anddriving a polarity reversing switch to provide a polarity adjusteddegraded signal which continually has the same polarity as that of thefirst derivative and which is integrated. It is contemplated that themagnitudes of the corrective signals to be added to the degraded signalbe adjustable to enable an operator to obtain a display exhibiting thebest subjective combination of contrast and edge sharpness.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a partial block andschematic diagram of an imaging system with display including enhancingcircuitry according to the invention;

FIG. 2 represents a timing diagram of various signals present in theapparatus of FIG. 1 when a bar of constant brightness is being scanned;and

FIG. 3 represents a timing diagram of various signals present in theapparatus of FIG. 1 when a series of equal width bars is being scanned.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, aconventional line-scan-imaging system 11 is focused to view a remoteobject 12 and provide an electrical analog output signal which varies inamplitude in accordance with the relative intensity of successiveportions of the particular line being scanned. Generally, the system 11provides, rather than an AC signal, an intensity varying DC signalsuitable for intensity modulating the visual output of a conventionalline scan display 13 such as a television monitor, the minimum intensitylevel usually corresponding to the dark current level for the imagingsystem. The apparatus for synchronizing the line scan display 13 withthe line scan imaging system I1 is conventional and is not shown inFIG. 1. Because of imperfections in the transmission path from theobject 12 to the system 11 such as turbulent air, because of imagemotion blurring or because of other reasons including imaging systembehavior which is similar to a low-pass spatial filter, the systemoutput signal may be degraded in that it may not be capable of causingthe system display 13 to reproduce the image of the object exactly as itreally is.

The degraded output signal of the system 11 is, therefore, applied toenhancing circuitry generally designated 20 to first and second,serially connected differentiators 22 and 23 which provide analog outputsignals 9 and j} generally indicative of, respectively, the first andthe second derivatives of the output signal of the system 11 hereinafterreferred to as the degraded signal, y. The degraded signal y along withthe output signals and yof the differentiators 22 and 23 are applied toedge sharpness and contrast enhancers for subjection to a type ofprocessing called janitizing.

The term janitizing as used herein means a process of making any signalvarying with respect to a reference level either always have the samepolarity as (plus janitizing) or always have an opposite polarity (minusjanitizing) with respect to any other signal varying relative to itsrespective reference level. Basically, janitizing is accomplished byapplying the two signals involved to a polarity comparator or detectorwhich provides an indication as to whether or not the input signals havethe same polarity relative to their respective reference levels. Thepolarity detector output signal is applied to a polarity reversingswitch to cause a polarity adjustment in the signal being janitized atthe appropriate times.

As will hereinafter be explained in greater detail, it is desired that acorrection signal of adjustable magnitude for enhancing edge sharpnessbe developed by minus janitizing" the first derivative of the degradedsignal with respect to the second derivative of the degraded signal.Additionally, it is desired to develop a second correction signal ofadjustable magnitude for enhancing image contrast by integrating theresult of plus'janitizing the degraded signal with respect to the firstderivative of the degraded signal. Accordingly, the output signals yandyof the differentiators 22 and 23, being both referenced to a level ofzero volts, are applied to a same polarity detector 24 in an edgesharpness enhancer 25. The output signal 9 of the differentiator 22 anda bias adjusted form y of the degraded signal y, having been rebiased tohave a predetermined reference level by a conventional variable biasadjuster 26, are applied to an opposite polarity detector 27 in acontrast enhancer 28. It is convenient to use a bias adjuster 26 capableof shifting to a reference level of zero volts that level of thedegraded signal y such as one which eliminates a background noise levelor bias level intensity y, or one which is midway between the darkcurrent and saturation current levels of the output signal of the systemI 1. Generally, the polarity detector 24 or 27 may be fabricated fromconventional digital logic circuits and includes conventional hardlimiter devices 30 and 31 or 32 and 33 for changing the applied inputanalog signal to digital form such as rectangular output waveformshaving level transitions corresponding in time to polarity reversals.

In the same polarity detector 24 in the edge sharpness enhancer 25, theoutput waveforms of the limiters 30 and 31 are each applied to anAND-gate 35 and to respective ones of a pair of inverters 36 and 37whose output signals, in turn, are provided to a second AND-gate 38. Theoutput signals of the AND-gates 35 and 38 are fed through an OR-gate 39and comprise the detector output signal which is, in turn, fed from thedetector 24 to cause when in a logical ONE state a reversal of thepolarity of the output signal of a conventional polarity reversingswitch 40.

The switch 40 is connected to receive as an input signal the firstderivative output signaly from the differentiator 22. The polarityreversing switch 40 may, for example, comprise a double pole,relay-driven switch controlled by the detector output signal and havinga pair of relay-driven contacts arranged to contact alternatively firstand second or second and third contact members, the first and thirdcontact members being electrically connected together. The minusjanitized analog output signal of the polarity reversing switch 40 isapplied through a conventional analog signal amplitude adjusting device41 such as an amplifier or an attenuator for introducing into theapplied analog signal a desired amplitude adjustment of magnitude oreither greater or less than one and providing the edge sharpnessenhancing correction signal 2, of desired magnitude.

In order to indicate that a signal have been plus or minus janitized thesymbology of the positive or negative subscript j, for the signal isadopted herein, the term n being any integer including zero whichcorresponds to the order of the derivative of the signal with respect towhich the signal is being janitized." For example, since the degradedsignal from the imaging system 11 has been designated y=f(t) and itsfirst derivative designated y, the minus janitized signal from theswitch 40 in the enhancer 25 is designated ti -J to indicate that thefirst derivative of y is to be minus janitized with respect to thesecond derivative of Y.

The opposite polarity detector 27 in the contrast enhancer 28 includes aconventional EXCLUSIVE OR-gate 42 receiving as input signals the outputsignals of the limiters 32 and 33 and providing a logical ONE as thedetector output signal when the detector input signals have oppositepolarity. Thev output signal of the opposite polarity detector 27 isapplied to control a second polarity reversing switch 43 of conventionaldesign connected to receive as an input signal the bias adjusteddegraded signal y from the bias adjuster 26. The plus janitized outputsignal from the reversing switch 43 is designated v. J wherein the primeindicates that the signal being plus janitized with respect to the firstderivative of y is the result of bias adjusting the degraded signal y,yequaling the instantaneous difference between y=f(l) and the intensityy A conventional analog signal integrator 44 is connected to receive asan input signal and provides an output signal which is applied, as inthe enhancer 25, to a conventional analog signal amplitude adjustingdevice 45 for scaling to introduce an amplitude adjustment of magnitude8 and provide the contrast enhancing correction signal z of desiredmagnitude.

The degraded signal y from the imaging system 11 is also applied forscaling to analog signal amplitude adjusting device 46 for introducingan amplitude adjustment I, greater or less than one, set at thediscretion of the operator. The signals z.. z, and P y from theadjusting devices 41, 45 and 46 are all combined by a conventionalanalog summing device 47 whose output signal y is applied through yetanother signal amplitude adjusting device 48 as a video signal to thedisplay 13 to intensity modulate its visual output. The output signal y,of the summing device 47 may be expressed as:

wherein the coefficients a, B and I correspond to the degree ofamplitude adjustment introduced by the adjusters 41, 45 and 46 as set bythe operator.

An operator can tune the enhancing circuits 20 by adjusting the outputlevels of the adjusters 41, 45 and 46 to provide that enhanced videosignal which enables the display 13 to exhibit a particular combinationor composite of contrast and edge sharpness subjectively considered bythe operator to be the best image. The intensity of the best compositeof contrast and edge sharpness is, of course, set to optimum conditionby setting the adjuster 48. The variable bias adjuster 26 is set toestablish a polarity reference level for the signal y such as to tuneout background noise in order that the portion of the signal y mostprobably attributable to the image being scanned can be processed toproduce the contrast enhancing signal. Alternatively, it may bedesirable in cases of images having repeated brightness variations toset the adjuster 26 so that the polarity reference level is establishedto correspond to the level which is midway between the maximum andminimum levels of brightness of the image.

Referring to FIG. 2, an example of processing the degraded output signaly=f( t) produced in response to scanning across an image having sharplydefined edges and a substantially constant intensity level may behelpful to an understanding of the apparatus of FIG. 1. Under the idealconditions, the imaging system 11 should provide a rectangular pulse Aof amplitude 111- whose width in time is a function of the scanning beamsweep velocity as shown in FIG. 2. Because conditions are not ideal, letit be assumed that the amplitude time characteristic of the degradedoutput signal y of the system 11 is substantially Gaussian and issuperimposed on a noise level of intensity y as shown in FIG. 2a.Accordingly, the degraded output signal y and its first and secondderivatives and yshown in FIG. 2 may be represented by the followingequations:

Minus janitizing y with respect to in the enhancer 25 prois applied tothe amplitude adjusting device 41. The enhancer output signal z,representing some magnitude or of the signal is as set by the operatoris summed with the degraded signal y in the summing device 47. Assumingin (l) that F=l and B=0, the output signal y, of the summing device 47has a form like that represented in FIG. 2. It should be noted that theoutput signal y not only substantially conforms in shape to therectangular pulse A as desired but also implied that all the spatialharmonics in the object are represented in the edge-sharpened imagealthough some harmonics have larger amplitudes than would be the case inthe ideal rectangular pulse.

In the event that the contrast of the displayed image is notsubjectively considered to be sufficient, the contrast enhancer 28 maybe operated to introduce more contrast without increasing the noiselevel. The bias adjuster 26 is set so that the noise level y,, iseliminated, producing y as indicated in FIG. 2. The output signal of theintegrator 44 may be expressed as generally may be considered asindicating the area under output signal of the switch 43, represented inFIG. 2. Summing the degraded signal y with some adjustable magnitude [3of the integrated janitized signal indicated as 2,, in FIG. 20,increases the relative amplitude of y, as is indicated in FIG. 2 by thecurve y, superimposed for comparison purposes over the representation ofthe degraded signal y. The resulting increase in contrast, of course,may be further increased over that provided by the ideal rectangularpulse A. The effect of combining both an edge sharpness enhancing signalz, and a contrast enhancing signal z, with the degraded signal y toproduce y, is represented in FIG. 2 wherein the brightness of the centerof the edge enhanced image is increased the greatest degree.

Referring to FIG. 3 as a further example, consider a repetitive imagecomprising a series of black bars interspersed with white spaces ofequal widths. Under ideal conditions, the signal y will be a rectangularwave shown in dashed lines in FIG. 3 and having a bias level y,equivalent to the average of the maximum and minimum intensities. TheFourier series for a 6). wave is, as a function of distance x:

21rmx wherein the bias intensity y equals half the sum of the maximumand minimum intensities, the contrast intensity y, equals half thedifference of the maximum and minimum intensities,

k=l /L (6) Substituting equation (6) and into equation (5) and expandingequation (5) provides the following equation (7): B=y,,+2y/1r[sin(21rkxH-l/3 sin 3(21rkx)+l/5 sin 5(21rkx)+. l (1) which illustrates thatthe ideal signal B as a function of distance x of the traversing scanincludes both the fundamental spatial frequency and its odd harmonics.Assuming that the line-scan-imaging system 11 has such poor transfercharacteristics that only the fundamental of the spatial frequencies ispassed, the higher harmonics being so attenuated as to be negligible,and assuming that the amplitude of the fundamental is substantially thesame as that of the ideal square waveform B, the degraded signal y as afunction of time becomes y=f(1)y,,+2yr/rr sin 21rkv t a wherein the termat of equation (7) has been replaced by the product v of the scanningbeam velocity v,, of the system 11 and time t. Accordingly, since thetemporal angular frequency w in radians per second may be representedby:

w=21rkv 9 equation (8) becomes y=f(t)a +2y l1r sin wt (l0) whosewaveform is indicated in FIG. 3 and which when applied to the display 13would normally yield a television monitor picture with poor edgeresolution because of blurring.

The missing or sharply attenuated odd harmonics of the degraded signalas indicated for the ideal case by equation (7) can be substantiallyrestored by the edge sharpness enhancer 25. The first and secondderivatives of equation 10) are:

whose waveforms are The signal expressed as the Fourier series generatedfrom equations l l) and I2) is [sin 9mt sin 11m] (13) to yield, for thecase wherein ,6==O:

whose waveform is represented in FIG. 3.

It can be seen from equation (14) that the janitized signal Y-flaccentuates the higher frequencies and therefore brings out details inthe visual display. Additionally, since the magnitude of is proportional.to the fundamental frequency, the characteristic may be used tocompensate for the falling off of spatial frequency response. The visualpicture provided by the display 13 can be made to appear more crisp byincreasing a.

As in the case for the Gaussian pulse, the contrast of the degradedimage can be increased by the enhancer 28 by accentuating the lowerfrequencies. Since the bias adjuster 26 removed the bias signal y fromthe degraded signal y of equation (10) to avoid, among other things, theproblem of adjacent image merger, the bias adjusted signal y' which isto be" plus janitized with respect to the first derivative y may beexpressed as:

y=2y,/1r sin wt whose waveform is indicated in FIG. 3. The signal is 1m) {(cos wt cos 3m) 3 (cos 5m whose waveform is represented in FIG. 3and which may be integrated and gain adjusted to develop the correctivesignal 2,

from the enhancer 28 which may be expressed in series forms as n+3] y jlt= {sin wt 1 sin 3 wt 0 ma 3 1 1 smSwtsin 7w2+. (l7) which isrepresented in FIG. 3. From the above, it appears that integrating thejanitized degraded signal produces a corrective signal 2 for addition tothe degraded signal y which emphasizes the low frequencies and whereinthe amplitude of the series varies inversely as the frequency. Assumingthat 0: equals 0, the output signal y, of the summing device 47 asindicated in FIG. Sis

sin 7wt+. (18),

which signal enables a display of greater contrast than does thedegraded signal y. This is true even though the fundamental may be soattenuated that the amplitude of the fundamental no longer equals thatof the rectangular waveform B which would be produced under idealconditions.

When both some magnitude [3 of the contrast enhancing signal 2 and somemagnitude (1 of the edge sharpening signal 2,. are present, the totalsignal y, from the summer 47 may be derived by combining equations (14)and 18) to provide the waveform of equation 19) aw B i 3 150,

whose waveform is indicated in FIG. 3h.-

It is to be noted from equation (19) that the coefficients of the termsof course determine the waveform of the resultant signal y. It isapparent for low frequencies that the a term of the coefficientdominates since the limit of the product aw approaches 0 as w approaches0 while the limit of the quotient. B/w approaches infinity as mapproaches 0. Correspondingly, for higher frequencies, the the (1 termsof the coefficients dominate since the limit of the product canapproaches infinity as w approaches infinity and the limit of thequotient B/w approaches 0 as m approaches infinity. The rate at whichthe limits are approached is, of course, determined by the relativemagnitudes of a and B which are set by the gain adjusters 41 and 45. Asindicated above, any desired combination of contrast and edge sharpnesscan be established by tuning the enhanced video signal from theadjusters 41 and 45. The final adjustment provided by the gain adjustingdevice 48 permitsthe display of maximum contrast within the dynamicrange of the display 13.

As may be indicated by the foregoing examples, the apparatus of FIG. 1is a valuable tool for analyzing the degraded output signals of imagingsystems. By adjusting the various gain adjustment devices 41, 45, 46 and48, an operator can scrutinize the display 13 and ascertain whichdegrees of contrast and crispness provide the best or most nearlyrecognizable display of the line-scan system output signal. Theapparatus avoids the defects of known contrast enhancing apparatus whichinherently increases not only the contrast level but also theaccompanying noise level because of straightforward amplification of thedegraded signal. As indicated in the above examples of contrastenhancement, the primary spatial frequencies involved are in arelatively low range, the noise being attenuated since it includes aprimarily spectra of higher frequencies. The enhancer 25 provides forincreased edge sharpness and picture crispness by taking advantage ofnot only the benefit of adding the first derivative of the degradedsignal but also the benefit of adding the sense of the negative of thesecond derivative without the deleterious effect of including the noisewhich would normally accompany/direct addition of the negative of thesecond derivative.

it may be desirable in some situations to modify the apparatus of FIG. 1as by processing a contrast enhanced, degraded signal with successiveenhancing circuitry including differentiators and an edge sharpness suchas 25. Additionally, it may be desirable tojanitize the degraded signalor one of its derivatives with respect to higher order derivatives thanthe first or second.

In some situations such as for a substantially repetitive image wherethe background noise level is greater than the maximum black indicatingsignal level, it may be desirable to bias the reference level of thecontrast enhancing signal z so that it has relatively negative portionswhich are combined to reduce the intensity of the degraded signal ry. Avariable bias adjuster, not shown, may be incorporated for the purposein the apparatus of FIG. 1 as by electrically interconnecting it betweenthe integrator 44 and the gain adjuster 45. Thereby, the reference levelof the signal z may be adjusted to a value intermediate the maximum andminii r intensities of z enabling the greatest degree of contrastbetween the points of maximum and minimum brightness in the displayedimage while remaining within the dynamic range of the display 13.

Obviously many modifications and variations of the present invention arepossible in view of the above teachings. It is therefore to beunderstood that within the scope of the ap pended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is: 1. Apparatus for processing an electrical inputsignal to provide a video signal comprising:

differentiating means adapted to receive the input signal for providingsignals indicated in the nth and the (n-i-k)th derivatives of the inputsignal wherein n is any integer including zero and k is any integergreater than zero; signal polarity adjusting means connected to saiddifferentiating means to receive said nth and (n+k )th derivative signalfor switching the polarity of said nth derivative signal to always bearan opposite polarity relative to the polarity of said (n+k)th derivativesignal and for providing an output signal linearly indicative of saidnth derivative signal switched in polarity opposite to the polarity ofthe (n-l-k)th derivative signal; and

signal summing means adapted to receive the input signal and connectedto said polarity adjusting means for adding the input and adjustingmeans output signals to provide the video signal.

2. Apparatus according to claim 1 further comprising:

integrator means electrically interposed between said polarity adjustingmeans and said signal-combining means integrating said polarity adjustedoutput signal of said polarity adjusting means.

3'. Apparatus according to claim 2 further comprising:

bias adjuster means connected to receive said nth derivative of theinput signal for adjusting its polarity reference level to a levelbetween the maximum and minimum intensities of the input signal andproviding an output signal indicative of said adjusted nth derivative tosaid polarity adjusting means.

4. Apparatus according to claim 1 wherein said signal polarity adjustingmeans comprises:

first polarity detector means for providing a detector output signalindicative that the polarities of said derivatives of said input signalmeasured relative to respective reference levels have a predeterminedrelative sense; and

first polarity reversing means normally providing as an output signalsaid nth derivative of the input signal and responsive to said detectoroutput signal for providing as said output signal said nth derivativesignal having a reversed polarity.

5. Apparatus according to claim 4 further comprising:

, said first detector means providing said output signal indicative thatsaid nth and (n-l-k) th derivatives have opposite polarity.

6. Apparatus according to claim 4 further comprising:

said first detector means providing said output signal indica- .tivethat said nth said (nk)th derivatives have the same polarity.

7. Apparatus according to claim 4 further comprising:

said means providing said derivative indicating signals including firstand second differentiating means serially connected for providingsignals indicative of respectively the first and the second derivativesof the input signal;

said first detector means providing said detector output signalindicative that said first and second derivatives have the samepolarity; and

said first polarity reversing means providing said first derivativesignal as polarity adjusted in response to said first detector outputsignal.

8. Apparatus according to claim 7 further comprising:

variable means for adjusting the magnitude of electrical signals appliedthereto and electrically interposed between said first polarityreversing means and said signal-combining means.

9. Apparatus according to claim 4 further comprising:

said means providing said derivative indicating signals providing thezero derivative of the input signal and including first differentiatingmeans for providing the firstderivative of the input signal;

said first detector means providing said detector output signalindicative that said zero and said first-derivative signals haveopposite polarities;

said first polarity reversing means providing said zeroderivative signalas polarity adjusted in response to said first detector output signal;and v integrator means electrically interposed between saidpolarity-reversing means and said signal combining means for integratingsaid polarity-adjusted zero-derivative signal.

10. Apparatus according to claim 9 further comprising:

variable means for adjusting the magnitude of electrical signals appliedthereto and electrically interposed between said integrator means andsaid signal-combining means.

11. Apparatus according to claim 9 further comprising;

said means providing said derivative-indicating signals furtherincluding second differentiating means for providing the secondderivative of the input signal;

second polarity detector means connected for receiving said first andsecond-derivative signals for providing a second detector output signalindicative that said first and second derivatives have the samepolarity; and

second polarity-reversing means providing to said signalcombining meanssaid first derivative signal as polarity adjusted in response to saidsecond detector output signal.

12. Apparatus according to claim 11 further comprising:

first, second, third, and fourth variable means for adjusting themagnitude of electrical signals and being respectively electricallyconnected for receiving and adjusting the input signal, for receivingand adjusting the output signal of said integrator means, for receivingand adjusting the output signal of said second polarity-reversing meansand for receiving and adjusting said output signal of saidsignal-combining means to provide the video output signal.

13. Apparatus according to claim 12 further comprising;

variable bias adjuster means connected to receive the input signal foradjusting its polarity reference level to a level between the maximumand minimum intensities of the input signal and providing an outputsignal indicative of said adjusted zero derivative to said firstdetector means and to said first polarity-reversing means.

14. Apparatus for processing an electrical input signal to provide avideo output signal comprising:

differentiating means adapted to receive the input signal for providingsignals indicative of the first and the second derivatives of the inputsignal;

signal polarity-adjusting means connected to said differentiating meansto receive said first and second derivative signal for switching thepolarity of said first derivative signal to always hear an oppositepolarity relative to the polarity of said second derivative signal andfor providing a first corrective signal linearly indicative of saidfirstderivative signal switched in polarity opposite to the polarity ofthe second derivative signal;

integrating means adapted to be connected to receive the input signalfor providing a second corrective signal indicative of the integrationof a polarity adjustment of the input signal which adjustment has apolarity the same as that of the first derivative of the input signal;and

signal summing means connected to said signal polarity adjusting andintegrating means for receiving and adding said first and secondcorrective signals with the input signal to provide the video outputsignal.

15. Apparatus according to claim 14 further comprising:

said signal polarity-adjusting and integrating means each includingvariable means electrically interposed for adjusting the relativemagnitude of the respective one of said first and second correctivesignals.

16. Apparatus according to claim 15 wherein said integrating meansincludes;

variable bias-adjuster means connected to receive the input signal foradjusting its polarity reference level and providing an output signal;

adjustment means receiving said bias-adjuster output signal forproviding said polarity adjustment having a polarity the same as that ofsaid bias-adjuster output signal; and

integrator means for receiving and integrating said polarity adjustmentto provide said second corrective signal.

1. Apparatus for processing an electrical input signal to provide avidEo signal comprising: differentiating means adapted to receive theinput signal for providing signals indicative of the nth and the (n+k)thderivatives of the input signal wherein n is any integer including zeroand k is any integer greater than zero; signal polarity adjusting meansconnected to said differentiating means to receive said nth and (n+k)thderivative signal for switching the polarity of said nth derivativesignal to always bear an opposite polarity relative to the polarity ofsaid (n+k)th derivative signal and for providing an output signallinearly indicative of said nth derivative signal switched in polarityopposite to the polarity of the (n+k)th derivative signal; and signalsumming means adapted to receive the input signal and connected to saidpolarity adjusting means for adding the input and adjusting means outputsignals to provide the video signal.
 2. Apparatus according to claim 1further comprising: integrator means electrically interposed betweensaid polarity adjusting means and said signal-combining means forintegrating said polarity adjusted output signal of said polarityadjusting means.
 3. Apparatus according to claim 2 further comprising:bias adjuster means connected to receive said nth derivative of theinput signal for adjusting its polarity reference level to a levelbetween the maximum and minimum intensities of the input signal andproviding an output signal indicative of said adjusted nth derivative tosaid polarity adjusting means.
 4. Apparatus according to claim 1 whereinsaid signal polarity adjusting means comprises: first polarity detectormeans for providing a detector output signal indicative that thepolarities of said derivatives of said input signal measured relative torespective reference levels have a predetermined relative sense; andfirst polarity reversing means normally providing as an output signalsaid nth derivative of the input signal and responsive to said detectoroutput signal for providing as said output signal said nth derivativesignal having a reversed polarity.
 5. Apparatus according to claim 4further comprising: said first detector means providing said outputsignal indicative that said nth and (n+k) th derivatives have oppositepolarity.
 6. Apparatus according to claim 4 further comprising: saidfirst detector means providing said output signal indicative that saidnth said (n-k)th derivatives have the same polarity.
 7. Apparatusaccording to claim 4 further comprising: said means providing saidderivative indicating signals including first and second differentiatingmeans serially connected for providing signals indicative ofrespectively the first and the second derivatives of the input signal;said first detector means providing said detector output signalindicative that said first and second derivatives have the samepolarity; and said first polarity reversing means providing said firstderivative signal as polarity adjusted in response to said firstdetector output signal.
 8. Apparatus according to claim 7 furthercomprising: variable means for adjusting the magnitude of electricalsignals applied thereto and electrically interposed between said firstpolarity reversing means and said signal-combining means.
 9. Apparatusaccording to claim 4 further comprising: said means providing saidderivative indicating signals providing the zero derivative of the inputsignal and including first differentiating means for providing thefirst-derivative of the input signal; said first detector meansproviding said detector output signal indicative that said zero and saidfirst-derivative signals have opposite polarities; said first polarityreversing means providing said zero-derivative signal as polarityadjusted in response to said first detector output signaL; andintegrator means electrically interposed between said polarity-reversingmeans and said signal combining means for integrating saidpolarity-adjusted zero-derivative signal.
 10. Apparatus according toclaim 9 further comprising: variable means for adjusting the magnitudeof electrical signals applied thereto and electrically interposedbetween said integrator means and said signal-combining means. 11.Apparatus according to claim 9 further comprising; said means providingsaid derivative-indicating signals further including seconddifferentiating means for providing the second derivative of the inputsignal; second polarity detector means connected for receiving saidfirst and second-derivative signals for providing a second detectoroutput signal indicative that said first and second derivatives have thesame polarity; and second polarity-reversing means providing to saidsignal-combining means said first derivative signal as polarity adjustedin response to said second detector output signal.
 12. Apparatusaccording to claim 11 further comprising: first, second, third, andfourth variable means for adjusting the magnitude of electrical signalsand being respectively electrically connected for receiving andadjusting the input signal, for receiving and adjusting the outputsignal of said integrator means, for receiving and adjusting the outputsignal of said second polarity-reversing means and for receiving andadjusting said output signal of said signal-combining means to providethe video output signal.
 13. Apparatus according to claim 12 furthercomprising: variable bias adjuster means connected to receive the inputsignal for adjusting its polarity reference level to a level between themaximum and minimum intensities of the input signal and providing anoutput signal indicative of said adjusted zero derivative to said firstdetector means and to said first polarity-reversing means.
 14. Apparatusfor processing an electrical input signal to provide a video outputsignal comprising: differentiating means adapted to receive the inputsignal for providing signals indicative of the first and the secondderivatives of the input signal; signal polarity-adjusting meansconnected to said differentiating means to receive said first and secondderivative signal for switching the polarity of said first derivativesignal to always bear an opposite polarity relative to the polarity ofsaid second derivative signal and for providing a first correctivesignal linearly indicative of said first-derivative signal switched inpolarity opposite to the polarity of the second derivative signal;integrating means adapted to be connected to receive the input signalfor providing a second corrective signal indicative of the integrationof a polarity adjustment of the input signal which adjustment has apolarity the same as that of the first derivative of the input signal;and signal- summing means connected to said signal polarity adjustingand integrating means for receiving and adding said first and secondcorrective signals with the input signal to provide the video outputsignal.
 15. Apparatus according to claim 14 further comprising: saidsignal polarity-adjusting and integrating means each including variablemeans electrically interposed for adjusting the relative magnitude ofthe respective one of said first and second corrective signals. 16.Apparatus according to claim 15 wherein said integrating means includes:variable bias-adjuster means connected to receive the input signal foradjusting its polarity reference level and providing an output signal;adjustment means receiving said bias-adjuster output signal forproviding said polarity adjustment having a polarity the same as that ofsaid bias-adjuster output signal; and integrator means for receiving andintegrating said polarity adjustment to provide said second correctivesignal.